The Mandelbrot set is a good candidate for GPU implementation: it's simple, uses vector math, and is embarrassingly parallel. Doing so, however, generally adds a significant amount of complexity to a program. The programmer is forced to twist all computations to fit within the graphics pipeline, and a significant amount of ceremony surrounds even the simplest operation.

The GPGPU framework in Penumbra is designed to get hide away all these rough edges, with the goal of making it easier to use the GPU for these sorts of tasks than it would be to use plain Clojure. It's not quite there yet, but in this particular example it proves to be extremely useful.